The invention relates to an optically readable code and to a method of marking printed circuit boards by means of an optically readable code.
Optically readable codas by which information is encrypted in symmetrical patterns or images in a compressed form are known. This type of code can be read out and decoded quickly and in an uncomplicated manner using simple scanner technologies.
The codes formerly used were almost exclusively one-dimensional codes, in particular so-called bar codes, in which the information is encoded in binary form in parallel bars of different widths.
More recently, two-dimensional codes are increasingly employed, which are structured, for example, in the form of a matrix or a grid and which, in terms of surface area, have a higher information density than one-dimensional codes. Known examples of two-dimensional codes include QR codes or DataMatrix codes.
The drawback of all these codes is that the resolution of the scanners is limited and, therefore, the codes must not be smaller than a specific minimum size. This results in that the codes can only be applied to sufficiently large surface areas and that the largest surface area available for marking limits the maximum amount of information that can be included in a code.
This limitation is a problem above all in the semiconductor industry since a unique identification of, for example, a printed circuit board solely on the baste of external features may be impossible later and therefore makes a marking absolutely necessary. Due to miniaturization, i.e. the tendency or effort made towards an ever decreasing accommodation space, the room available therefor is limited, especially in the case of printed circuit boards.